Potassium thiosulphate

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: No standard test, but test well described and relevant ecological endpoint for evaluation the effect of thiosulfate on the N-cycle is evaluated (effect on urea hydrolysis).

Justification for type of information:

see attachment “Read-across concept – Human Health/Environment - Category approach for Inorganic sulfites/thiosulfates/dithionite" in section 13.

Principles of method if other than guideline:

ATS was added to urea-spiked soils, and urea levels were extracted and determined after 3 and 10 days using methods described by Douglas and Bremner (1970) and Mulvaney and Bremner (1979).

Details on preparation and application of test substrate:

The soils used were surface (0-15 cm) samples of Iowa soils selected to obtain a range in properties (Webster, Hayden, Harps, Storden). Each sample was air-dried and crushed to pass through a 2-mm screen

Test organisms (inoculum):

other: not specified

Total exposure duration:

10 d

Remarks:

samples were also analysed after 3 d

Test temperature:

20 degrees Celcius

Moisture:

2 mL in 5 gram of dried soil

Details on test conditions:

Five gram samples of air-dried soils were placed in 65-mL glass bottles and treated with 2 mL of water containing 10 mg of urea or with 2 mL of water containing 10 mg of urea and various amounts of the test compound. The bottles were stoppered and placed in an incubator at 20°C. After 3 and 10 days, triplicate bottles were removed from the incubator, and urea in the incubated soil samples was extracted and determined by a colorimetrc method.

Nominal and measured concentrations:

Nominal mg ATS/kg soil: 500, 1000, 2500, 5000

Duration:

3 d

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Webster, Harps, Storden soil

Duration:

3 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Hayden soil

Duration:

3 d

Dose descriptor:

other: LOEC

Effect conc.:

2 500 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Webster, Harps, Storden soil

Duration:

10 d

Dose descriptor:

NOEC

Effect conc.:

2 500 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Webster soil

Duration:

10 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Hayden, Harps, Storden soil

Duration:

10 d

Dose descriptor:

other: LOEC

Effect conc.:

5 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: retardation of urea hydrolysis

Remarks on result:

other: Webster soil

Details on results:

ATS significantlly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil).

Conclusions:

The effect of ammonium thiosulfate on urea hydrolysis was investigated in urea-spiked soils that were exposed to different concentration levels of ATS. ATS significantlly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil). These data can be used as supportive information for the assessment of thiosultfates in the terrestrial compartment.

Additional information

In a supporting study by McCarty et al. (1990), the effect of ammonium thiosulfate on urea hydrolysis was investigated in urea-spiked soils that were exposed to different concentration levels of ammonium thiosulfate. Ammonium thiosulfate significantly retarded urea hydrolysis only when applied at rates as high as 2500 or 5000 mg/kg soil (NOEC: 2500 mg/kg soil), which are significantly above the OECD test limit of 1000 mg/kg soil. Thus, results indicate a low potential for the toxicity of thiosulfate substances on microbial nitrogen cycling in soil.